Hydraulic system and method



Nov. 10, 1964 E.V.MANN1NG HYDRAULIC SYSTEM AND METHOD Filed Aug. 28, 1962 A uw INVENTOR 'EDWARD v. MANMNG BY '@5/ MW ATTORNEYS United States Patent O Jersey Filed Aug. 28, 1962, Ser. No. 219,915 8 Claims. (Cl. 1123-479) This invention relates to hydraulic starting systems for engines, and more particularly to improved means for automatically terminating operation of the starter after the engine has reached starter cut-out speed.

This application is a continuation-in-part of my copending application Serial No. 201,067, filed June 8, 1962, now abandoned.

The co-pending application of Melvin L. Kent and Edward V. Manning, Serial No. 119,170, liled lune 23, 1961, discloses a hydraulic starting system utilizing a variable displacement starter motor which is `supplied with motive fluid from a constant pressure source of limited iiow capacity. By reason of the limited capacity of the pump in the source, or, in the case where the source pump is larger than required, by reason of a llowlimiter in the supply path to the motor, the maximum rate of supply to the motor is limited to a value equal to the demand of the motor when it is operating at maximum displacement and at a certain speed less than cut-out speed. This certain speed is approm'mately equal to the ignition speed of the engine. As the motor accelerates the engine from rest to ignition speed, its ow demand increases and this demand is satised by the increasing supply from the source. At ignition speed, the supply rate of the source is a maximum and, therefore, continued acceleration of the motor tends to impose a flow demand on the source which exceeds its capability. The system of application Serial No. 119,170 includes a motor control that reduces motor displacement during acceleration from ignition speed to cut-out speed so that the flow demand of the motor in this phase of the starting cycle is maintained substantially constant and equal to the maximum supply rate of the source.

The object of this invention is to provide a method and mechanism for terminating operation of the starter motor, in a system employing a constant pressure source of motive fluid, when the engine reaches starter cut-out speed without requiring a direct measurement of engine speed. According to one form of the invention, the starter motor is a variable displacement unit and the ystarting system is the type disclosed in application Serial No. 119,170. In this embodiment, the minimum displacement of the motor is limited to a value greater than zero so that when the engine reaches starter cut-out speed the motor control will no longer be able to maintain flow demand constant by reducing motor displacement. Since the supply rate to the motor is limited (either by the capacity of the source pump or by a flow limiter), the operating pressure of the motor will decrease as soon as the engine reaches starter cut-out speed. In accordance with this invention, the supply of fluid to the motor is interrupted when this change in motor operating pres- Transmission `of torque from the'engine to the motor is prevented and, therefore, when the supply of fluid to the motor is interrupted, the motor comes to rest and imposes no load on the engine as the latter accelerates from cut-out speed. YIn essence, this control Fice terminates operation of the motor when the engine reaches cut-out lspeed without requiring a direct measurement of that speed.

The second form of the invention is essentially the same as the rst, but it uses a fixed displacement starter motor. In this case, the maximum rate of supply of the source is limited, either by the capacity of the source pump itself or by a ilow limiter, to a value equal to the demand of the motor at starter cut-out speed. Thus, as in the rst embodiment, attainment yof starter cut-out speed is accompanied by a decrease in motor operating pressure and this change initiates termination of motor operation.

Two embodiments of the invention are described herein with reference to the accompanying drawing in which:

FlG. 1 is a schematic diagram of a starting system according to the invention employing a variable displacement starter motor.

FIG. 2 is a schematic diagram of a starting system according to the invention employing a xed displacement starter motor.

As shown in FlG. 1, the starter system comprises a variable displacement starter motor 2 having high and low pressure ports 3 and d, respectively, which are connected with the supply conduit 5 and reservoir 6, and a drive shaft 7 which is coupled to the engine 8 through a drive connection indicated at 9. The drive connection 9 contains a one-way overrunning clutch 11 arranged to ltransmit torque from the motor 2 to the engine S but not in the opposite direction. Motor 2 is of the rotary cylinder barrel longitudinally reciprocating piston type and includes a cam plate 12 that is angularly adjustable about the axis of trunnion 13 between minimum and maximum displacement-establishing positions. A stop 14 defines the minimum displacement establishing position and limits the minimum displacement of the motor to a value greater than zero. The stop, therefore, prevents overspeeding of the motor V2,.

Cam plate 12 is biased in the clockwise direction about trunnion 13 toward the minimum displacementestablishing position by a spring 15 and is shifted in the opposite direction by a piston motor 16 having a working chamber 17. Fluid is admitted to and exhausted from working chamber 17 through conduit 1S under the control of a pilot valve 19 which is connected with reservoir 6 through conduit 21 and with supply conduit 5 through conduit 22. The pilot valve Y19 responds to the operating pressure of motor 2 land serves to transmit fluid from supply conduit 5 to working chamber 17 when operating pressure is above a predetermined value and to vent working chamber 17 to reservoir 6 when operating pressure is below that value. When operating pressure is at said predetermined value, pilot valve 19 assumesa lap position in which working chamber 17 is isolated from both conduit 5 and reservoir 6 and motor 16 is hydraulically locked. The pilot valve illustrated in application Serial No. 119,170 may be used in this system. Although pilot valve 19 of the motor control responds to motor operating pressure, it Will be apparent that, from a functional standpoint, this control actually regulates the displacement of motor 2 in accordance with its iiow demand.

Motive iiuidfor driving motor 2 is derived from a constant pressure source thatincludes a variable delivery, discharge pressure compensated pump 23 which is driven by a prime mover 24, such as an auxiliary engine, and whose high and low pressure ports 25 and 26, respectively, are connected with the supply conduit and the reservoir 6. The pump 23 may be of the variable displacement rotary cylinder barrel, longitudinally reciprocating piston type, such as the motor-pump unit of application Serial No. 119,170. Located in the supply conduit 5 is a solenoid-operated start valve 27 which is biased closed and is opened when its solenoid 27a is energized. Upstream of this valve 27, the supply conduit 5 joins a delivery conduit leading to a hydraulic system for operating auxiliary apparatus.

In the FIG. 1 embodiment, it is assumed that the maximum delivery rate of pump 23 is greater than the demand of motor 2 when the latter is operating at the ignition speed of engine and cam plate 12 is in the maximum displacement-establishing position. Therefore, in this case, the rate of supply to motor 2 is limited to that demand by a flow limiter 29 interposed in supply conduit 5. The illustrated location of iow limiter 29 in the supply path to motor 2 is not critical and, as a matter of fact, it usually is most convenient to mount it in the casing of the motor in the passage between high pressure port 3 and the motor working chambers. However, if the ow limiter is mounted in the casing of motor 2, the pilot valve 19 and the pressure switch described below, both of which respond to motor operating pressure, must still be connected with the supply path downstream of the llc-w limiter.

The solenoid of start valve 27 is connected in an electrical circuit including battery 31 and switch 32. The switch is biased in the opening direction by a spring 33 and is urged in the closing direction by a pressure responsive motor 34 that is connected with the supply conduit 5 downstream of ow limiter 29 by conduits 35 and 22.

When switch 32 is open, and consequently valve 27 is closed, the starter motor 2 and its control are isolated from the source and the pressure in conduit 5 downstream of Valve 28 is low. Therefore, pilot valve 19 assumes the vent position in which working chamber 17 of motor 16 is connected with reservoir 6, and spring holds cam plate 12 in its minimum displacementestablishing position against stop 14. If prime mover 24 is running, pump 23 will discharge Huid to delivery conduit 28 and its displacement will be regulated in accordance with the demands of the auxiliary hydraulic equipment so that discharge pressure is maintained substantially constant.

In order to start engine 8, the operator closes switch 32 to thereby energize solenoid 27a and cause it to open start valve 27. Fluid discharged by pump 23 now Hows to motor 2 through conduit 5 and the pressure in this conduit and in conduits 22 and 35 immediately rises. The operator may now release switch 32 since motor 34 will hold it closed. In response to this change in pressure, pilot valve 19 moves to the supply position and transmits fluid under pressure to working chamber 17 through conduits 22 and 18. Motor 16 now moves cam plate 12 to its maximum displacement-establishing position against the bias of spring 15. The fluid supplied to motor 2 causes it to drive engine S through shaft 7, overrunning clutch 11 and drive connection 9.

As motor 2 accelerates engine 8, its iiow demand increases. Since pump 23 includes a discharge pressure compensator, it satisfies this demand and maintains supply pressure (i.e., the pressure upstream of llow limiter 29) substantially constant by increasing the delivery of pump 23. When engine 8 reaches the speed at which it is ignited, the flow demand of the motor 2 equals the maximum rate of supply as determined by iow limiter 29. Therefore, as the engine commences to develop assisting torque and to accelerate from ignition speed, the demand of motor 2 exceeds the rate of supply and, consequently, motor operating pressure, i.e., the pressure downstream of the ow limiter, tends to decrease. Pilot valve 19 senses this change in pressure and shifts to the vent position, thereby allowing spring 15 to move cam plate 12 toward its minimum displacement-establishing position. When the change in ilow demand produced by the speed increase is oilset by the decrease in motor displacement, pilot valve 19 moves to the lap position and motor 16 becomes hydraulically locked and holds cam plate 12 in a reduced displacement position. As engine 3 continues to accelerate, the motor control continues to effect a reduction in the displacement of motor 2 in an eoit to maintain its flow demand constant at the rate demanded at ignition speed.

When engine 8 reaches starter cut-out speed, the controls for motor 2 will have moved cam plate 12 to the minimum displacement-establishing position defined by stop 14E. Since, at this time, both the displacement of and the ow to motor 2 are limited, the acceleration of the motor begins to lag the acceleration of the engine 8 and motor output torque decreases. Therefore, a slight increase in the speed of engine 8 will be accompanied by a pronounced decrease in motor operating pressure and spring 33 will open switch 32. Valve 27 now closes and interrupts the supply of iiuid to motor 2. As a result, motor 2 comes to rest and remains idle until the operator again closes switch 32. Because of the presence of overrunning clutch 11, the motor 2 imposes no load on the engine and the latter may, therefore, accelerate rapidly from starter cut-out speed.

In the preceding discussion, it is mentioned that the motor control commences to move cam plate 12 toward the minimum displacement-establishing position when engine Snreaches ignition speed. While it is possible to operate the system in this manner, it is preferred to design pump 23, or, in the case where pump 23 is oversize, to design flow limiter 29 to establish a maximum delivery rate that enables motor 2 to operate at maximum displacement until the engine reaches a speed slightly higher (for example, 1000 r.p.n1. higher) than the recommended ignition speed. This procedure insures that the starter will be developing maximum torque when the engine is ignited without requiring the operator to initiate ignition at a precise speed.

The second embodiment of the invention, shown in FIG. 2, employs a lixed displacement starter motor 2 of the rotary cylinder barrel longitudinally reciprocating piston type. In this case, of course, the cam plate 12' is xed. The source of motive fluid in this system employs a pressure compensated pump 23 which, it is assumed, has a maximum rate of delivery greater than the demand of motor 2 at starter cut-out speed, and a iow limiter 29 that limits the maximum supply rate to this demand. As in the irst embodiment, the iiow limiter can be eliminated in those cases where the maximum output of the pump equals the ow rate established by the flow limiter.

The starting cycle of the FIG. 2 system is essentially the same as the starting cycle of the FIG. l system except that the displacement of motor 2 is fixed and its demand increases continuously up to starter cut-out speed. When switch 32 is closed momentarily, start valve 27 opens and allows the fluid discharged by pump 23 to pass to and through motor 2' thereby causing it to accelerate engine Motor operating pressure, which is transmitted to motor 34 through conduit 35', maintains switch 32 closed after it is released by the operator. As motor 2 accelerates, its demand increases, and, unlike the FIG. 1 embodiment, this increase continues beyond ignition speed. When engine 3 reaches starter cut-out speed, motor 2' will be demanding the maximum rate of liow permitted by flow limiter 29. Therefore, at this point the acceleration of motor 2 begins to lag the acceleration of engine 3 and motor output torque decreases. As a result, a slight increase in the speed of engine 8 will be accompanied by a marked decrease in motor operating pressure and spring 33 will open switch 32 and terminate the supply of iiuid to motor 2'. As in the preceding embodiment, the starter motor 2' now comes to rest and engine 8 accelerates rapidly to its normal operating speed.

The drawing and description relate only to two illustrative embodiments of the invention, Since many changes can be made in these embodiments without departing from the inventive concept, the following claims should provide the sole measure of the scope of the invention.

What I claim is:

1. ln combination, an engine and a hydraulic starting system for accelerating the engine to starter cut-out speed, the system comprising (a) a variable displacement hydraulic motor including a displacement control element movable between minimum and maximum displacement positions;

(b) stop means defining a minimum displacement position for the displacement control element in which the displacement of the motor is greater than zero;

(c) drive means connecting the motor and the engine and arranged to transmit torque from the motor to the engine;

(d) means associated with the drive means for preventing the transmission of torque from the engine to the motor;

(e) a source of hydraulic fluid capable of delivering iiuid at -a substantially constant pressure and at a rate which varies between a minimum value and a maximum value equal to the demand of the motor when the displacement control element is in maximum displacement position and the motor is operating at a speed less than starter cut-out speed;

(f) conduit means connected with the motor and the source for leading iiuid from the source to and through the motor;

(g) motor control means responsive to the ow demand of the motor for maintaining the displacement control element in the maximum displacement position when the motor is running and the demand is below said maximum delivery rate and for moving the displacement control element toward the minimum displacement position when the demand tends to exceed said maximum delivery rate to thereby maintain the iiow demand constant at that rate; and

(h) means responsive to the operating pressure of the motor for terminating the supply of fluid from the source to the motor when the operating pressure decreases below a predetermined value.

2. The combination deined in claim l in which the last-mentioned means comprises (a) a shut-oli valve located in the condui-t means; and

(b) means responsive to the operating pressure of the motor for closing the shut-off valve.

3. The method of accelerating an engine to starter cut-out speed using a variable displacement hydraulic motor comprising (a) generating fluid under pressure and supply-ing same to the motor to cause it to accelerate the engine;

(b) maintaining supply pressure substantially constant as the rate of supply is varied from a minimum value to a maximum value;

(c) operating the motor at maximum displacement until the engine accelerates to a certain speed less than starter cut-out speed;

(d) starting the engine at least by the time it reaches said certain speed so that it commences to develop assisting torque;

(e) limiting the maximum rate of supply to the motor to the rate demanded by the motor at said cer-tain speed; t

(j) reducing the displacement of the motor as the engine accelerates from said certain speed to thereby maintain motor demand constant at the demand imposed at said certain speed;

(g) limiting the minimum displacement of the motor to a value greater than zero;

(h) terminating the supply of iiuid to the motor when motor operating pressure decreases as a result of motor demand exceeding said maximum supply rate; and i (i) preventing the transmission of torque from the engine to the motor.

4. In combination, an engine and a hydraulic starting system for accelerating the engine to starter cut-out speed, the system comprising (a) a iixed displacement hydraulic motor;

(b) drive means connecting the motor and the engine and arranged to transmit torque from the motor to the engine;

(c) means associated with the drive means for preventing the transmission of torque from the engine to the motor;

(d) a source of hydraulic iiuid capable of delivering iiuid at a substantially constant pressure and at a rate which varies between a minimum value and a maximum value equal to the demand of the motor at starter cut-out speed;

(e) conduit means connected with the motor and the source for leading iiuid from the source to and through the motor; and

(f) means responsive to the operating pressure of the motor for terminating the supply of uid from the source to the motor when the operating pressure decreases below a predetermined value.

5. The combination defined in claim 4 in which the last-mentioned means comprises (a) a shut-ofi valve located in the conduit means; and

(b) means responsive to the operating pressure of the motor for closing the shut-oli valve.

6. The method of accelerating an engine to starter cut-out speed using a fixed displacement hydraulic motor comprising (a) generating fluid under pressure and supplying same to the motor to cause it to accelerate the en- $1116;

(b) maintaining supply pressure substantially constant as the rate of supply is varied from a minimum value to a maximum value;

(c) starting the engine when it reaches a certain speed less than cut-out speed so that it commences to develop assisting torque;

(d) limiting the maximum rate of supply to the motor to -the rate demanded by the motor at starter cut-out speed;

(e) preventing the transmission of torque from the engine to the motor; and

(f) terminating the supply of iuid to the motor when motor operating pressure decreases as a result of motor demand exceeding said maximum supply rate.

7. In combination, an engine and a hydraulic starting system for accelerating the engine to starter cut-out speed, the system comprising (a) a hydraulic motor whose displacement always is greater than zero;

(b) drive means connecting the motor and the engine and arranged to transmit torque from the motor to the engine;

(c) means associated with the drive means for preventing the transmission of torque from the engine to the motor;

(d) a source of hydraulic fluid capable of delivering Huid at a substantially constant pressure and at a rate which varies between a minimum value and a maximum value not greater than the demand of the motor at starter cut-out speed;

(e) conduit means connected with the motor and the sburce for leading fluid from the source to and through the motor; and

:risas-aa (f) means responsive to the operating pressure of the :motor for terminating the supply of fluid from the source to the motor when the operating pressure decreases below a predetermined value.

8. The method of accelerating an engine to starter cut- 5 out speed using a hydraulic motor whose displacement always is greater than zero comprising (a) generating uid under pressure and supplying same to the motor to cause it to accelerate the engine;

(b) maintaining supply pressure substantially constant 10 as the rate of supply is varied from a minimum value to a maximum value;

(c) starting the engine when it reaches a certain speed less than cut-out speed so that it commences to develop assisting torque;

(d) limiting the maximum rate of supply to the motor to a rate not greater than that demanded by the motor at starter cut-out speed;

(e) preventing the transmission of torque from the engine to the motor; and

(f) terminating the supply of uid to the motor when motor operating pressure decreases as a result of motor demand exceeding said maximum supply rate.

No references cited. 

1. IN COMBINATION, AN ENGINE AND A HYDRAULIC STARTING SYSTEM FOR ACCELERATING THE ENGINE TO STARTER CUT-OUT SPEED, THE SYSTEM COMPRISING (A) A VARIABLE DISPLACEMENT HYDRAULIC MOTOR INCLUDING A DISPLACEMENT CONTROL ELEMENT MOVABLE BETWEEN MINIMUM AND MAXIMUM DISPLACEMENT POSITIONS; (B) STOP MEANS DEFINING A MINIMUM DISPLACEMENT POSITION FOR THE DISPLACEMENT CONTROL ELEMENT IN WHICH THE DISPLACEMENT OF THE MOTOR IS GREATER THAN ZERO; (C) DRIVE MEANS CONNECTING THE MOTOR AND THE ENGINE AND ARRANGED TO TRANSMIT TORQUE FROM THE MOTOR TO THE ENGINE; (D) MEANS ASSOCIATED WITH THE DRIVE MEANS FOR PREVENTING THE TRANSMISSION OF TORQUE FROM THE ENGINE TO THE MOTOR; (E) A SOURCE OF HYDRAULIC FLUID CAPABLE OF DELIVERING FLUID AT A SUBSTANTIALLY CONSTANT PRESSURE AND AT A RATE WHICH VARIES BETWEEN A MINIMUM VALUE AND A MAXIMUM VALUE EQUAL TO THE DEMAND OF THE MOTOR WHEN THE DISPLACEMENT CONTROL ELEMENT IS IN MAXIMUM DISPLACEMENT POSITION AND THE MOTOR IS OPERATING AT A SPEED LESS THAN STARTER CUT-OUT SPEED; (F) CONDUIT MEANS CONNECTED WITH THE MOTOR AND THE SOURCE FOR LEADING FLUID FROM THE SOURCE TO AND THROUGH THE MOTOR; (G) MOTOR CONTROL MEANS RESPONSIVE TO THE FLOW DEMAND OF THE MOTOR FOR MAINTAINING THE DISPLACEMENT CONTROL ELEMENT IN THE MAXIMUM DISPLACEMENT POSITION WHEN THE MOTOR IS RUNNING AND THE DEMAND IS BELOW SAID MAXIMUM DELIVERY RATE AND FOR MOVING THE DISPLACEMENT CONTROL ELEMENT TOWARD THE MINIMUM DISPLACEMENT POSITION WHEN THE DEMAND TENDS TO EXCEED SAID MAXIMUM DELIVERY RATE TO THEREBY MAINTAIN THE FLOW DEMAND CONSTANT AT THAT RATE; AND (H) MEANS RESPONSIVE TO THE OPERATING PRESSURE OF THE MOTOR FOR TERMINATING THE SUPPLY OF FLUID FROM THE SOURCE TO THE MOTOR WHEN THE OPERATING PRESSURE DECREASES BELOW A PREDETERMINED VALUE. 